1. Field of the Invention
The present invention relates to a radiation image capturing apparatus including a radiation detector for detecting charge information representing radiation image information. More specifically the present invention relates to a radiation image capturing apparatus which processes a signal from the radiation detector to prevent deterioration in the image quality of the radiation image.
2. Description of the Related Art
In the medical field, radiation image capturing apparatus is extensively used which exposes a subject (patient) to radiation and detects the radiation that has passed through the subject with a radiation detector in order to acquire a radiation image.
One example of such a radiation image capturing apparatus includes a radiation detector having linear electrodes formed therein. Charge information representing an electrostatic latent image stored in the radiation detector is read out by applying reading light that is perpendicular to the longitudinal direction of the linear electrodes over the length of the electrodes (see, for instance, the description of U.S. Pat. No. 4,857,723 and Japanese Laid-Open Patent Publication No. 2000-287034).
The description of U.S. Pat. No. 4,857,723 is directed to a radiation detector used in image capturing apparatus of the type described above. The radiation detector detects a current generated by each pixel when LED light is applied to the linear electrodes simultaneously as charge information representing the electrostatic latent image, and outputs the charge information via an analog multiplexer and an analog/digital converter (hereinafter referred to as an “A/D” converter).
Japanese Laid-Open Patent Publication No. 2000-287034 discloses a method and an apparatus for solving problems relating to the configuration recorded in U.S. Pat. No. 4,857,723. Specifically, the analog multiplexer recorded in the description of U.S. Pat. No. 4,857,723 causes deterioration in image quality due to noise generated when switching between pixel signals. To solve this problem, Japanese Laid-Open Patent Publication No. 2000-287034 proposes the provision of a different A/D converter for each linear electrode.
From Japanese Laid-Open Patent Publication No. 2000-287034, it is clear that the invention recorded in the description of U.S. Pat. No. 4,857,723 has a problem caused by noise when switching between signals in the analog multiplexer. In addition, there are concerns about how the responsiveness of an analog amplifier provided downstream of the analog multiplexer affects the image information. In particular, when an increase in overall throughput speed necessitates an increase in the switching speed of the analog multiplexer, problems such as blurring and loss of sharpness in image caused by poor responsiveness of the analog amplifier, occur at image edges and other portions with high contrast.
According to the invention recorded in Japanese Laid-Open Patent Publication No. 2000-287034, however, an analog multiplexer is not required and so the problems caused by noise when switching between signals in an analog multiplexer are eliminated. However, the invention of Japanese Laid-Open Patent Publication No. 2000-287034 has a disadvantage in that when an A/D converter is provided for each linear electrode rather than being provided singly in the manner of U.S. Pat. No. 4,857,723, the increase in scale of the printed circuit board leads to increases in occupied space and cost.